Marine vessels in use today use marine propulsion systems that typically include the following sub-systems: an engine to provide power, a transmission to transfer drive power to a propeller, and a control system to provide control of engine speed and transmission engagement. An operator or pilot of the vessel nominally has control of the engine speed and transmission shifting through one or more operator controls. Using these operator controls, the transmission can be shifted between forward and reverse, usually through a neutral (transmission disengaged) position, and the engine speed can be set as desired by the operator.
Engine stalling is a problem sometimes encountered when operating a marine vessel, and often this occurs when the vessel is moving in one direction at high speed and the operator suddenly shifts the transmission into the opposite gear. The stall is the result of the linear momentum of the vessel moving through the water which imparts a drag load on the propeller that tends to keep the propeller, transmission, and engine rotating in the same direction. Reversing the transmission under these circumstances, however, places a sudden increased load on the engine because of the drag load on the propeller. As a result, the engine is often unable to overcome the sudden increased load and, therefore, the engine stalls.
Another problem can arise when a pilot attempts to avoid the engine stalling problem. Faced with a potential engine stall, a pilot will often “race” the engine prior to shifting it into the reverse gear. Racing the engine, however, can lead to transmission clutch damage caused by excessive engine speed prior to full engagement of the transmission clutch to the engine. To avoid damage to the transmission, marine transmission manufacturers recommend maximum acceptable engine speeds (typically 1,000 RPM) for all transmission shifts including neutral to forward or reverse, and forward or reverse through neutral to the opposite gear. Exceeding the maximum acceptable engine speed during a shift tends to result in excessive clutch temperatures and possibly clutch failure.
Attempts to alleviate the above problems usually involve using electronic controls, or “blind timers”, to delay the time between shifting the transmission and increasing of the speed of the engine to allow the transmission clutch to fully engage the engine and propeller driveshaft. This method is only effective under specific conditions, such as where the drag load on the propeller decreases by a sufficient amount during the time delay such that the engine can overcome the sudden increased load without stalling. In some instances, however, this method may be ineffective because the shift is not delayed long enough and the engine stalls, or because the delay is too long resulting in an unnecessarily long shift delay.